Papers by Keyword: Surface Crack

Abstract: For the description of cracks in rolling/sliding contacts many overlapping interactions has to be regarded and most of them are non-linear phenomena. This paper emphasis the aspect of plasticity around cyclically loaded shear cracks which is omitted very often in the common literature. It is shown that this plasticity can be calculated and regarded in computed crack driving forces; however, the problem is not solved after doing this. It is a first estimate only to regard the crack driving force calculated in the finite elements surrounding the crack tip as a relevant measure.

Abstract: In this paper, the plate with different surface cracks (different constraints) was selected, the finite element numerical simulation method was used to mod el the J-integral and the equivalent plastic strain (ε_p) distributions ahead of crack front, after the unified constraint characterization parameter A_p was calculated, a new parameter which considered both J-integral and constraint effect was defined and a new methodology was provided to ensure the maximum crack extension location of surface crack. The results show that if the location of the maximum is defined as the maximum crack extension location, the prediction results is consistent with the measured results in experiments. The parameter which considered both crack driving force and material resistance force is a suitable parameter, and can be used to predict the maximum crack extension location.

Abstract: Fatigue crack growth rate at the plane stress is predicted by Paris equation, associating it with the stress intensity factor (SIF), generalized parameter of the elastic stress field near the crack tip. The finite element method allows modelling of the incremental crack growth in the plates, where the finite element grid should be re-meshed on each crack growth step fitting the first principal stress planes. However, the linear fracture mechanics format (LEFM) based evaluation of the two-dimensional fatigue cracks does not provide always the correct crack front assessment and appropriate life-predictions. It is shown that approach using the damage accumulation simulation and strain-life criterion may be promising in analysis of the two-dimensional cracks. Application of the approach is illustrated. The simulation results are in good agreement with the experimental data.

Abstract: This paper presents a numerical investigation on semi-elliptical surface cracks in round bars subjected to mode III loadings. Lack of information can be found in open literature regarding to the J-integral solution especially the surface crack subjected to mode III loadings. Therefore, this work investigates and analyzes crack behavior using J-integral approach. On the other hand, a mathematical model is also developed to predict the J-integral along the crack front. It is found that the J-integral can be used to predict well along the crack front. However, the prediction is strongly influenced by whether the material is elastic-or plastic dominated region.

Abstract: Depth of evaluation method of surface crack in laser cladding coating with metal magnetic memory was introduced in this paper. Laser cladding coating specimen were degaussed, placement direction of specimen and detection direction unchanged, detection speed and lift off value of probe were the constant. Results show that gradient value of H_p(y) signal corresponding to surface crack increases as tensile load increases under the same depth of surface crack, gradient value of H_p(y) signal corresponding to surface crack increases as depth of surface crack increases under the same tensile load. Orientation of internal magnetic domain changes as tensile load changes and magnetic leakage field caused by surface crack are seen as two main reasons for above results. Using fitting method with quadratic polynomial, depth of surface crack in laser cladding coating can be evaluated nondestructively in this paper.

Abstract: An acquisition of ferrite surface images has been taken with a LY-WN-YH Hyper-depth measurement system, from which the crack condition was analyzed with MATLAB. Based on the contradistinction between experimental data from ferrite work pieces of different quality, a preliminary conclusion has been drawn that the surface quality of ferrite materials has a direct link to the quantity and length of the crack on them. By measuring the quantity and length of the crack, an initial criterion was obtained for judging the surface quality of ferrite.

Abstract: The traditional identification method of surface crack has some shortcomings such as detection equipment complex, high requirements for operator and not suitable for large-scale structure inspection, vibration method is applied to identify surface crack in steel rods in this paper, using the method of calculating modal analysis combined with time-frequency wavelet analysis. The research on damage identification is performed on steel rods with different deep crack. The research results show that the accurate damage location can be judged by wavelet modulus maximum and the quantitative analysis of single crack identification can be achieved by constructing mathematical expressions of a single crack damage degree and damage index Lipschitz index. The research would province some guidance for engineering applications.

Abstract: In order to reveal the failure mechanism of TiN coating, the simulations of scratch process with finite element method are carried out. Meanwhile, the stress analysis was carried out on the three stages that stylus tip indenting coating surface, slipping on coating surface and rising from coating surface. Through the observation of simulation results and the analysis of the stress shows that there are two ways of forming coating surface cracks. One is that coating interface cracks are firstly induced, thus they are propagated to the coating surface, and finally the surface cracks are formed. Other is that cracks are directly formed in coating surface. Because they are induced by maximum tensile stress, surface cracks are modeI.After stylus tip rising from coating surface, biggish residual stresses remain in the coating. Those analyses will supply the basis of coating design and application.

Abstract: The inclined surface cracks are under the mixed mode I,II,III loading conditions. Direct tension experiments of brittle materials with surface crack have been carried out. The crack growth process, fracture pattern and the initiation angle of the surface crack were attained. In order to analyze the mixed-mode fracture criterion of the surface crack in brittle materials stress intensity factor of the crack front of the surface crack was calculated based on the FRANC3d firstly. And then the minimum strain energy density criterion, the maximum circumferential stress criterion and the revised maximum circumferential stress criterion were used to calculate the initiation angle. The revised maximum circumferential stress criterion proved to be fit for the attained experimental results.

Abstract: The aim of this paper is to present the simulation technique and experimental work for surface crack in a structure. For the sake of test apparatuss feasibility, a semielliptical surface crack in a structure was converted into small specimen size. The specimens represented semielliptical surface crack problem in real application of engineering structure. The specimens with semielliptical surface crack were tested by experiment and simulation. The S-version Finite Element Model (S-FEM) was implemented in simulation, and verification was performed through experimental works. The S-FEM consists of virtual crack closure method and Paris law as a crack growth criterion for 3-dimensional problem with hexahedron elements was used. Auto-mesh generation technique with a fully automatic crack growth simulation system was employed in S-FEM simulation. Specimens with 0^o of crack surface angle were prepared and analysed for the mode I loading. A four-point bending fatigue test was conducted and simulated in order to gain crack path, fatigue crack growth and stress intensity factors value. Results from simulation and experiment showed good agreement with a certain condition. The implications from the results were discussed through the analysis of fatigue crack growth.